This invention relates to syringes, and more particularly to a syringe construction designed for the prevention of needle-stick injuries. Hypodermic syringes are widely used to inject substances into human beings and animals. A hypodermic syringe typically includes a barrel for containing the substance to be injected, and an injection needle which is connected to the barrel. Hypodermic syringes are frequently disposable, and thus are normally discarded after use to avoid spread of contamination or disease. It has been observed that there is a low but ever-present rate of needle-stick injuries suffered by medical practitioners after a syringe has been used. In one study of needle-stick injuries published recently, Rates of Needle-stick Injury caused by Various Devices in a University Hospital, J. Jagger, M.P.H., Ph.D., E. H. Hunt, R.N., J. Brand-Elnaggar, B.A., & R. D. Pearson, M.D.; 319 New England Journal of Medicine, 284-288 Aug. 4, 1988, the disposable syringe resulted in 6.9 needle-stick injuries per 100,000 items purchased, and accounted for 35 percent of the total number of needle-stick injuries from all sources. The most common mechanism of injury from disposable syringes was due to attempts by hospital personnel to place a cap over the needle after use of the syringe. The study concluded that efforts to implement safety guidelines have been ineffective and are unlikely to eliminate such injuries in the future. The study proposed no actual solutions, but recommended redesign of instruments to eliminate use of needles, provide some sort of fixed barrier between the user and the needle, or allow the user's hands to remain behind the needle as it is covered.
This is an important recommendation since hypodermic needles, particularly used needles-even those which have been used only once, may be a threat to the health and safety of persons who must use them. Although an initial needle-stick injury may be minor, the possibility of infection is serious enough to warrant efforts to eliminate the possibility of a needle-stick injury entirely.
A wide variety of differing hypodermic syringes have been proposed in an attempt to prevent needle-stick injuries. These structures generally require modification of the syringe barrel.
U.S. Pat. No. 4,737,144 to Choksi discloses a syringe with a sleeve which can be locked in a retracted position and also an extended position. The locking mechanism includes a slot formed near the end of the barrel which cooperates with spring urged tabs on the sleeve.
U.S. Pat. No. 4,425,120 to Sampson, et al., discloses a needle guard mounted on the barrel of the syringe. The guard can be releasably locked in the retracted position or locked in the extended position. Locking of the guard is effected by a track on the internal surface of the guard and track-engaging members on the barrel.
U.S. Pat. No. 4,573,976, also to Sampson, et al., discloses a similar structure with different locking means. U.S. Pat. No. 4,356,822 to Winstead-Hall discloses a syringe assembly having a barrel and tubular guard with multiple locking members provided for securing the barrel and cap in a number of relative axial positions. A frangible end closure may be provided on the end of the cap closest to the needle. The locking members permit different locked positions for exposing different amounts of the needle.
Another approach is to provide a shield integral with the needle instead of the barrel. U.S. Pat. No. 3,134,380 to Armano discloses a collapsible needle guard integral with the needle portion of the syringe. The needle with guard is assembled and sterilized by the manufacturer. The purpose of the guard is to shield the needle from the view of the patient.
None of these structures are known to be in widespread use. Most standard hypodermic syringe assemblies presently in use are unshielded and do not resolve the problem of needle sticks.